About SARS-CoV-2 virus

• The SARS-CoV-2 is a corona virus which is a large family of viruses with some causing less severe common cold to more severe diseases such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).
• It is the causative agent of COVID-19 influenza which has been declared as a pandemic outbreak.

• Like other corona viruses, SARS-CoV-2 virus particles are spherical and have mushroom-shaped proteins called spikes protruding from their surface, giving the particles a crown-like appearance. 
• The spike binds and fuses to human cells, allowing the virus to gain entry.
• The spike protein of the SARS-CoV-2 binds to the cellular receptor called angiotensin-converting enzyme 2 (ACE2), which serves as the entry point into human cells. 

• But unlike in the case of SARS, the spike protein of the novel corona virus binds to the cell receptor with much higher affinity — 10- to 20-fold higher.
• The much greater binding affinity to the cell receptor explains the apparent high human-to-human transmissibility of the virus compared with the SARS corona virus.

Why in News?

Ever since cases of ‘reinfection’ — people who had tested negative for COVID-19 testing positive again after a while — the question of latency of the SARS-CoV-2 virus is being hotly debated.

What is latency of a virus?

• A latent infection is when the virus in the body is dormant or inactive and does not replicate within the host. 
• It however possesses the capacity to be reactivated at some point, causing a flare-up of the disease much later.
• The latent viral infections can be reactivated into a lytic form, in which there is replication of the viral genome.
• The latent (or persistent; but not chronic) infections are essentially static which last the life of the host and occur when the primary infection is not cleared by the adaptive immune response.
• Examples are Herpes simplex viruses type 1 and 2, varicella-zoster virus, HIV, Epstein-Barr virus (human herpesvirus 4), and cytomegalovirus. 

Two categories of virus

• Viruses fall into two broad categories: chronic and acute; while a chronic virus will infect its host for extended periods of time, often through the lifetime of the host. 
• An acute infecting virus, such as influenza and rotavirus, is cleared from the body after a few days or weeks.
• A chronic virus can go into latency.

Does SARS-CoV-2 go into latency? 

• There have been numerous cases around the world of people who got cured of Covid-19 testing positive for the infection again.
• Some experts have observed that the COVID-19 virus may have “reactivated” in the patients rather than them becoming re-infected.
• However, the latency of SARS-CoV-2 has not yet been established conclusively.

Reference:

1. https://www.thehindu.com/sci-tech/health/the-hindu-explains-is-sars-cov-2-a-latent-virus-which-can-recur/article32192853.ece